Mitigation of color loss or dye damage is a key element of fabric care. Historically, leaching of dyes from fabric produced an inexorable fading problem which has been largely overcome by the use of modem fabric substantive dyes, inter alia, “azo-dyes”. One drawback of azo dyes relates to the interaction of these dye molecules with heavy metals found in water. Dissolved metals, copper, inter alia, interact with fabric dye molecules thereby shifting the fabric dye emission spectra and producing a diffuse rather than a sharp, narrow emission band hue. Although the dye molecule itself is still present on the fabric, the result of this heavy metal/dye interaction is an appearance of color loss or fabric fading.
Polyamine chelants, inter alia, polyethyleneimines, have been used as chelants to suppress the activity of unwanted heavy metals. However, one drawback to the use of polyamines is their capacity to also chelate metal atoms which are a part of the dye molecule itself, for example, phthalocyanine dyes. This chelation of dye-based metals also results in the attenuation of fabric color. One solution is to strictly limit the amount of polyamine chelant used in detergent formulation to an amount which is sufficient only to chelate and remove unwanted heavy metals in the laundry liquor.
But polyamines which serve as chelating agents are also effective scavengers of fugitive bleaches. Bleaches are ruinous to dyed fabric because they can chemically alter dye molecules thereby producing non-colored molecules. The polyamines scavenge bleaches by reacting with the bleaches to form N-oxides or N-chloro polyamines depending upon the type of fugitive bleach. The reaction of polyamines with bleaches produces a modified polyamine thereby reducing or otherwise nullifying the usefulness of the polyamine as a chelant. Therefore, the formulator is left with the problem of deciding the proper amount of chelant to use. Not every consumer will be faced with the same level of fugitive bleach, therefore, a formulation which anticipates heavy bleach scavenging will provide excess polyamine in a non-bleach context, an excess of polyamine which can react pejoratively with the fabric dye molecules. On the other hand, a composition comprising an insufficient amount of polyamine chelant will not have a sufficient amount present to insure chelation of unwanted heavy metals and thereby ameliorate any color loss due to heavy metal/fabric dye association.
There is a long felt need for a laundry detergent composition or fabric care additive composition which will effectively mitigate the fabric dye damage caused by fugitive bleaches while allowing the formulation of polyamine chelants in an amount necessary to remove unwanted heavy metal ions.